Form Over Speed - In That Order
I don't know why, but sometimes when I work out, I feel pressure to go through the entire workout as fast as possible. I'm not sure if my brain is saying "the faster you go, the better the workout", but my brain's wrong. Even though high-intensity workouts keep your heart rate up, that shouldn't cost you you're form and control. And don't get me wrong, sometimes focusing on going slow can be a little frustrating when you just want to get the workout over. But I promise your body will thank you for it.
Why? I'll tell you.
Form > Speed
Perfecting form. I mean, think about it--compare it to school. You don't just start class at a 400 level. You start in basic courses and work your way up. Working out is the same. You teach your body the basics and continue practicing until you're ready for something more intense. Perfecting your form helps your body develop muscle memory, so your form will remain when you can go faster.
Preventing injury. No one wants to hurt themselves...and when you take it slow, you're way less likely to do so. If you continually do quick and jerky movements throughout a workout, your chances of injury are much higher, and once you're hurt you're out. You don't want to erase all that progress waiting to recover, right?
Preventing wrong muscle development/overcompensation. This goes hand-in-hand with the above point. If you don't have the correct form, sometimes your body will overcompensate by using the surrounding muscles. This means that the muscles that you think you're targeting are not actually getting stronger.
Building larger muscle mass. Slow lifts build muscles better than quick lifts. This happens because when you go slower, you keep the targeted muscles activated for a longer period of time. This goes against thinking that high intensity delivers the best workout, but it makes sense when you think about it.
Anyone can do it. Just because you're going slower, doesn't mean you need to increase weight. Use whatever you're comfortable with and work through the motions at your own pace. This will create a better, more effective workout until you've perfected your form and you're ready to pick up the pace.